1. Technical Field
The technical Field relates to barrier units used to protect lenses, and so on, of still cameras and video movie cameras.
2. Related Art
JP-A-5-27301 discloses a conventional barrier unit. According to the barrier unit, an excellent blocked state can be obtained using two blades of substantially the same shape.
FIG. 12 is a cross-sectional view of a conventional general barrier unit, taken along an optical axis direction. The barrier unit includes a cover 1 having an opening portion 1a that allows light C to incident therethrough; and a pair of first and second blades 2 and 3 that can open and close the opening portion 1a of the cover 1. The blades 2 and 3 are provided symmetrical to each other with an optical axis E therebetween. In an open state of the pair of blades 2 and 3 as shown in FIG. 12, predetermined end faces 2a and 3a which are parallel to the optical axis direction retreat outside the opening portion 1a of the cover 1, and in a closed state the predetermined end faces 2a and 3a contact each other.
Meanwhile, the end faces 2a and 3a of the first and second blades 2 and 3 may generally easily reflect light. Particularly, when the first and second blades 2 and 3 are made of metal pressed parts, the reflection may easily occur. For example, as shown in FIG. 12, when the blades 2 and 3 are in an open state, light C incident through the barrier unit reflects off the end faces 2a and 3a and the reflected light incident through a barrel, so that optical problems such as flare and ghosting may occur.
Reflection of the light C at the end faces 2a and 3a can be prevented by setting to a sufficiently the amount of retreat d of the blades 2 and 3 from the perimeter of the opening portion 1a of the cover 1 with the blades 2 and 3 being in an open state, large value. However, setting the amount of retreat d to a large value inhibits miniaturization of the barrier unit. In addition, by making the thickness t of the blades 2 and 3 sufficiently thin, reflection of light at the end faces 2a and 3a can be reduced. However, when the thickness t of the blades 2 and 3 is made thin, the amount of engagement between the end faces 2a and 3a in a thickness direction with the blades 2 and 3 being in a closed state is reduced. Hence, when, as shown in FIG. 13, the positions of the blades 2 and 3 are slightly displaced in the thickness direction, the end faces 2a and 3a do not contact each other and accordingly the blades 2 and 3 are likely to ride on top of each other. That is, there is a problem that a failure of opening and closing of the blades 2 and 3 is likely to occur.
To solve the above-described problems, a barrier unit is provided that can prevent a pair of blades from riding on top of each other when the blades are in a closed state. Another object is to provide a barrier unit that can suppress light from reflecting off end faces of blades when the blades are in an open state.